Engineering Board Exam Reviewer · Complex Numbers: Operations · medium

Find the modulus of (3+4i)(5-12i).

1. 18
2. 8.06
3. 4225
4. 65

Answer

D. 65

Solution

The modulus of a product is the product of the moduli: |3+4i|·|5-12i|=5·13=65.

More Complex Numbers: Operations questions

1. Evaluate (1+i)8.
2. Simplify 5+5i/1-2i.
3. Simplify (3+2i)(4-5i).
4. Simplify: i2001
5. Simplify: i15+i18
6. Add: (3+5i)+(2-7i)
7. Multiply: (4+3i)(2-i)
8. Divide: 3+4i/1-2i
9. Find the absolute value (modulus) of 5-12i.
10. Find the complex conjugate of 6-8i, then multiply it by the original number.

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